1. Field of the Invention
The present invention relates in general to stable compositions for inhibiting dental plaque and calculus formation and more particularly to oral compositions containing a combination of active zinc in the form of zeolitic zinc ions and fluoride ions. The invention particularly relates to toothpaste compositions having the aforesaid characteristics.
The presence of zinc compounds in oral products has been recognized for many years as beneficial for a variety of reasons. Zinc oxide and zinc phosphate were proposed as stabilizers in dental creams in U.S. Pat. No. 3,622,662 issued in November 1971 In U.S. Pat. No. 3,095,396 it is proposed to incorporate zinc salts into dentifrice formulations to inhibit the dissolving action of sodium metaphosphate. More recently, the zinc ion has been found to inhibit the formation of plaque and its consequent calcification to form calculus (tartar). Combination of zinc salts with enzymes, with antibacterial agents and with tetradecylamine are disclosed in U.S. Pat. Nos. 4,082,841; 4,022,880; and 4,146,607, respectively, for such purposes. Zinc carboxymethyloxysuccinate is utilized for its antiplaque and anticalculus properties in compositions proposed in U.S. Pat. No. 4,144,323.
For a period of many years, however, it was believed that zinc salts were only effective if present in dental formulations having pH values which are distinctly acidic in order to prevent the formation of the nearly insoluble, and thus ineffective, zinc hydroxide. The zinc ion itself tends to impart an organoleptically unpleasant astringency to dentifrices and other oral compositions, and when coupled with the sour taste characteristic of acidic compositions, the unpleasant taste was not readily tolerated. In efforts to avoid the disadvantages of zinc salts, it has more recently been found that the addition of glycine (aminoacetic acid) to oral compositions containing zinc salts permits the ambient pH to be increased to a range of 4.5 to 8.0, thus avoiding much of the astringency previously experienced while maintaining the zinc in a biologically active form. Such compositions are disclosed in U.S. Pat. No. 4,339,432 issued July 13, 1982 to Ritchey et al.
A still more recent advance has been made by the introduction of the zinc ions into oral compositions in the form of crystalline zinc aluminosilicates, i.e., zinc-exchanged zeolites. Not only is the biologically active zinc effectively provided by in situ ion exchange, but also other functions important to dental compositions such as abrasion of plaque and polishing as well as the creation of localized warmth by rehydration can be provided by the same constituent, thereby making formulation easier. A discussion of the benefits of using zeolites with therapeutic metal cations including zinc is set forth in U.S. Pat. No. 4,349,533 issued Sept. 14, 1982 to A. L. Dent et al. The use of zeolites in the alkali metal or ammonium cation form as anticorrosive agents is also described in U.S. Pat. No. 4,193,987.
In addition to antiplaque and anticalculus agents, it has for many years been the widely accepted practice to include in dentifrice and other oral compositions an anticariogenic agent, especially a water soluble fluorine-containing anticariogenic material. It is desirable to employ a sufficient quantity of the fluorine compound such that the concentration as the soluble fluoride in the dentifrice is from 600 to 1000 ppm (weight). Typically, the fluoride compound is sodium fluoride (NaF), stannous fluoride (SnF.sub.2) or sodium monofluorophosphate (Na.sub.2 PO.sub.3 F). Ideally the formulation of the dentifrice is such that essentially all of the fluorine compound employed is able to provide all of its fluorine value in the form of effective fluoride ion so that the total fluorine content of the dentifrice can be kept at a minimum and still provide the degree of anticariogenic activity essential for good dental health. Excessive amounts of fluorine can be seriously toxic when ingested, the degree of toxicity varying considerably among the various fluorine compounds.